NO149031B - ADDRESSING AGENTS FOR DENTALS AND PROCEDURES FOR ITS MANUFACTURING - Google Patents

Description

The present invention relates to improved abrasive preparations for dental care products. More particularly, the present invention relates to new, alkaline earth treated, felted silicon oxide abrasives which are suitable for use in therapeutic toothpaste preparations containing both soluble fluoride salts as enamel dissolution reducing agents and soluble phosphate salts as periodontal film penetrating agents. The invention further relates to a method for producing these improved field silicon oxide abrasives.

The function of an abrasive in preparations intended for use in the oral cavity is to remove various deposits, including membrane film, from the surface of the teeth. Membrane film is tightly adherent and often contains brown or yellow pigments and thus gives the teeth an ugly appearance. An advantageous toothpaste abrasive should provide maximum film removal without impacting

unnecessary grinding of the hard tooth tissue. Dental researchers are constantly busy developing toothpaste abrasives that show satisfactory levels of cleaning and that are not unnecessarily abrasive

and harmful to the oral tissue.

In addition to abrasives, therapeutic toothpastes typically contain fluoride ion sources. The beneficial reduction in the incidence of dental caries resulting from the local application to tooth enamel surfaces of solutions containing fluoride ions is well known. Especially at solution pH values between 4 and 8, fluorine ions are assumed to react with enamel and reduce the acid solubility of such enamel. Enamel treated in this way with fluoride is more resistant to the formation of dental caries. Accordingly, therapeutic toothpaste preparations are formulated to provide fluoride ion availability in brushing solutions formed in the oral cavity during use.

It has been postulated that the effectiveness of fluoride treatment in providing enamel antidissolution/anticariogenic benefits depends on the amount of fluoride ion available for uptake by the enamel being treated. It is, of course, therefore desirable to produce toothpaste preparations which provide maximum fluoride ion availability in brushing solutions formed therefrom. However, attempts to use such ionic fluoride anticariogenic agents in toothpastes suitable for home use have not been able to provide the theoretical maximum soluble fluoride due to the tendency of ionic fluoride to be inactivated and thereby made unavailable for enamel uptake. That is that toothpastes lose, on storage (at rates that increase with temperature), the ability to provide the theoretical maximum amount of soluble fluoride. In this description, the term "soluble fluoride" content of a given toothpaste preparation refers to the ppm concentration of fluoride ion present in the supernatant sample centrifuged from a 1:3 "by weight" suspension of the toothpaste in water (1:3 = toothpaste:water ).

Fluoride ion sources are prone to react with toothpaste contaminants and with such toothpaste ingredients as abrasives, buffers, etc. Such reaction reduces the fluoride source's ability to provide "soluble fluoride" in use. The tendency of toothpaste preparations herein to maintain their content of soluble fluoride after storage is herein expressed as "toothpaste-fluoride compatibility". The toothpaste-fluoride compatibility of a particular toothpaste preparation is thus the percentage of the theoretical maximum amount of fluoride source that is actually measured as soluble fluoride after storage for a specified time and at a specified temperature (e.g. 1 week at 49°C). Likewise, the propensity of such a dental care ingredient as the abrasive to react with the fluoride source and decrease the measured "soluble fluoride" level

from the theoretical maximum amount of fluoride source (especially in the presence of film film penetrants described in detail below) expressed as "abrasive fluoride compatibility". Experimental - The method used herein to determine "toothpaste fluoride compatibility" values and "abrasive fluoride compatibility" values is described more fully below.

A toothpaste ingredient that can create particular difficulties in the composition of fluoride toothpastes is a fused silicon oxide abrasive ingredient. Felt silicon oxide abrasives are desirable for use in toothpastes as they have desirable low dentin abrasive values. Certain previously known field silicon oxide abrasives are generally compatible with soluble fluoride sources, but have insufficiently high abrasive action to provide effective cleaning results. Certain other previously known field silicon oxide abrasives give acceptable cleaning results are,

but has low abrasive/fluoride compatibility as measured by the below-

end method. It is believed that no previously known field silicon oxide abrasives provide both high "abrasive/fluoride compatibility" as well as acceptable cleaning effects (as indicated by the standard "Radioactive Dentin Abrasion values"). There is thus a clear need to formulate field silicon oxide abrasives which exhibit high "abrasive/fluoride compatibility" as well as acceptable cleaning effects. It is consequently an aim of the present invention to provide field silicon oxide abrasives which exhibit high "abrasive/fluoride compatibility" as well as acceptable cleaning effects.

Another toothpaste ingredient that can be particularly harmful to the soluble fluoride content of certain toothpaste preparations is soluble phosphate. Soluble phosphate salts serve, when toothpaste is used, to increase the ability of the fluoride ions to penetrate the dental membrane film. For this reason, it is desirable to use soluble phosphate salts in fluoride toothpaste preparations. Especially in combination with silicon oxide dental abrasives, however, soluble phosphate membrane penetrants tend to promote the loss of soluble fluoride in toothpastes containing these materials, and thus the toothpastes exhibit low toothpaste/fluoride compatibility values. There is thus a clear need to compose field silicon oxide abrasives which provide high toothpaste/fluoride compatibility when used in fluoride toothpastes containing soluble phosphate salts as membrane film penetrants.

It has surprisingly turned out that the above objectives can be achieved by the present invention which provides a new field of silicon oxide abrasive which has been treated with an alkaline earth material, particularly calcium. By using the present dental abrasives, fluoride toothpastes, particularly those embodiments containing soluble phosphate salts, can be prepared which have high toothpaste/fluoride compatibility and excellent cleaning action.

It is of course well known that therapeutic toothpaste preparations contain calcium phosphate materials as abrasives, but these calcium materials are present in large quantities as described above and illustrated e.g. in the U.S. patents 3,624,199 and 3,864,471-There are also known toothpaste preparations containing small amounts of alkaline earth metal ions, such as calcium ions, and preparations of this type are illustrated by U.S. Pat. patent 3,991,177. This patent describes toothpaste preparations containing a stabilizer-activator for a dextranase enzyme agent, the stabilizer-activator being a. salt such as calcium chloride which is present in an amount of 0.001 to 0.3 wt. This preparation may also contain therapeutic fluoride, and the abrasive is calcium carbonate.

Other publications that disclose toothpaste compositions containing alkali metal compounds or ions include U.S. Pat. patents 3,095,356, 3,122,483, 3,669,221, 3,782,446, 3,842,168

and 3,689,537. None of these patents, however, relate to therapeutic toothpaste preparations containing as an abrasive a low-structure field silicon dioxide containing 10 to 300 parts per million of alkaline earth metal ion as described here.

The present invention provides a new abrasive material for dental care agents, especially for toothpastes, comprising a field, amorphous silicon dioxide produced by acidifying a fresh water alkali metal silicate solution and containing alkaline earth metal ions, and the abrasive preparation is characterized by the fact that the silicon dioxide has been intimately reacted with a compound of an alkaline earth metal so that there are 10-300 ppm alkaline earth metal ions in it and intimately associated with it, the amorphous silicon dioxide having an RDA value ("Radioactive Dentin Abrasion" value) of at least 40, a volume density of 0.24-0, 55 g/ml, an oil absorption of 70-95 cm 3 /100 g, a BET surface area of 100-250 m 2 /g, a loss on ignition of 4-6% and an average particle size of 5-15 µm, and in that the abrasive composition, when used in toothpastes containing a therapeutic fluoride agent, provides a paste exhibiting minimal loss of soluble fluoride upon storage at normal temperatures, and a f fluoride compatibility for the toothpaste of at least 90%.

The invention also relates to a method for the production of the abrasive preparations according to the invention, where

a) an aqueous solution of an alkali metal silicate with a molar ratio SiO2:X20 of 2.0-2.7, where X denotes an alkali metal, is prepared at a reaction temperature of 77-91°C, b) the alkali metal silicate solution is acidified with a mineral acid until the precipitation of silicon dioxide is essentially complete, after which the mineral acid addition is continued until the pH is 6.0 or below, c) digestion is carried out by heating at a temperature which is 10-30°C higher than the reaction temperature, for 10-30 minutes ,

and

d) the obtained slurry is filtered, and the solid product is washed with fresh water,

and the procedure is characterized by the fact that

e) the obtained wet cake is re-slurried in water and under stirring conditions, f) a sufficient amount of alkaline earth metal ions is added in the form of a sufficiently soluble alkaline earth metal compound in a sufficient amount so that alkaline earth metal ions are added to the wet cake in an amount of 10 300 ppm, based

on the dry recoverable product in the slurry,

g) the resulting mixture is stirred so that the effective amount of the alkaline earth metal adheres to the surface of the silicon dioxide, and h) the solid abrasive preparation is dried and recovered.

Fluoride-containing toothpaste preparations that include the amorphous,

felt silica abrasives of the present invention, a source of fluoride ions, a binder, a humectant and water, provide a pH of from 4.0 to 8.0 when slurried with water in a 3:1 water/preparation weight ratio. Such toothpaste preparations have been sought for protection in the divisional patent application 790502.

The present abrasive compositions are low-structure field silicon dioxide materials. The abrasive preparations according to the invention preferably contain 10 - 100 ppm alkaline earth metal ions, preferably calcium ions, calculated on the amount of extractable, dry material. The abrasive preparation also preferably exhibits an RDA value of from 70 to 120.

The dental abrasive materials according to the invention are fused silicon dioxide which is produced by general methods described e.g. in the U.S. patents 3 893 840 and 3 988 162. Abrasives produced by such methods are then treated with alkaline earth metal ions in the manner described here. In general, the process for the production of silicon dioxide comprises acidifying an aqueous alkali metal silicate solution with a mineral acid to effect refinement of the silicon dioxide. The acid addition is continued to an acidic pH, and the formed silicon dioxide is removed, e.g. by filtration and washed to remove any by-product materials such as alkali metal sulphate, whereby a wet cake is obtained.

The resulting wet cake is then reslurried in its own water or with additional water and then treated with the required amount of alkaline earth metal ions in the form of a soluble salt to obtain the abrasive materials according to the invention.

The abrasive products according to the present invention must be kept separate from the felt silicon dioxide preparations which have been treated with alkaline earth metal ions as described in Norwegian patent application 773160. Silicon dioxide treated with alkaline earth metals as indicated are abrasives which are useful for incorporation into toothpaste preparations to prevent corrosion of uncoated aluminum toothpaste tubes. Such corrosion-inhibiting field silicon dioxides as described in Norwegian application 773160 are silicon dioxides produced by a so-called sulphate liquid method. In the aforementioned method, an electrolyte such as alkali metal sulphate is mixed with alkali metal silicate liquid during acidification with mineral acid as described e.g. in US patents 3 960 586 and 3 928 54l• Although the products according to Norwegian application 773160 can be described as fused silicon dioxides intimately mixed with a quantity of alkaline earth metal ions which are within the scope of the present invention, the abrasives according to the present invention have different properties from the silicon dioxides obtained from sulphate - the liquid method. Liquid sulfate silicon dioxide materials do not, when used in certain fluoride-containing toothpaste preparations, provide the better fluoride compatibility values of the present invention. The better fluoride compatibility values of the dental abrasives according to the invention are only achieved with silicon dioxides produced from a so-called fresh water alkaline silicate method as described here.

The silicon dioxide abrasives according to the present invention are alkaline earth metal treated felt silicon dioxides which are prepared from fresh water silica top solutions. Such a method does not make use of any electrolyte such as sodium sulfate in the production of the untreated, fused silicon dioxide. It has further been found, in the products according to the invention, that the presence of alkaline earth metal ions intimately associated with the formed silicon dioxide must be present within a particularly narrow range to provide the fluoride compatibility necessary for use in the present invention. The abrasive products according to the present invention consequently have fluoride compatibility values of at least 90%, while the abrasives according to Norwegian patent application 773160 generally give compatibility values of 89% or lower, determined by the toothpaste/fluoride compatibility tests described here.

It is believed that the improved fluoride compatibility of the present dental abrasives is based on the manner in which the silanol groups therein are connected to the surface of the silicon dioxide product. In the freshwater silicate-containing silicon dioxide according to the present invention, the silanol groups on the surface of the material are thus assumed to be more accessible than on sulfate liquid silicate-derived silicon dioxide as described in Norwegian application 773160. Furthermore, the surface acidity of the freshwater silicon dioxides, due to the silanol groups, higher than the corresponding acidity of silicon dioxides obtained from the sulphate-liquid process. Because the silanol groups are different in the two materials, the actual surface acidity does not respond well to calcium treatment for fluoride compatibility in the sulfate liquid products. The products according to Norwegian application 773160 also have higher grinding values than the silicon dioxide according to the present invention. Existing abrasives must therefore be kept separate from the alkaline earth metal-treated silicon dioxide specified in Norwegian application 773160.

Present field silicon dioxide abrasives are produced by introducing an aqueous solution of an alkali metal silicate solution, preferably a sodium silicate solution, into a reactor for acidification. The aqueous sodium silicate solution is a fresh water solution with a sodium silicate concentration in the range of 10-17% by weight, and preferably 12.5 to 15.5% by weight and a sodium silicate composition of Na 2 O.2.6 SiC 2 for best results. The aqueous sodium silicate solution is then heated to a temperature of 50-95°C, and under: continuous stirring, the solution is acidified by the addition of an aqueous solution of a mineral acid with a concentration of 10-20 by weight at a substantially constant pH in the range of 8 .5 to 10.5. The mineral acid is preferably sulfuric acid as sulfuric acid gives the best results, but as is known in the art (see U.S. patents 3,988,162 and 3,983,840) other acidifying agents such as nitric acid, phosphoric acid, hydrochloric acid, carbonic acid and the like can also be used.

In the most preferred embodiment, only a part of the alkali metal silicate solution is introduced into the reactor, brought to the specified temperature with stirring, and the sulfuric acid and the rest of the alkali metal silicate solution are added simultaneously to the initial silicate solution at the reaction temperature. Preferably, 8 to 12% by weight of the metal silicate is initially introduced into the reactor. The remaining part is then added with the sulfuric acid. The time during which the alkali metal silicate and sulfuric acid are added to the alkali metal silicate in the reactor can be predetermined and is generally based on the volume of the reactor and the difficulties in controlling the temperature and agitation. After the addition of the alkali metal silicate solution is finished, the acidifying agent is added continuously until the pH of the reaction slurry falls below 6.0, and preferably to within the range 4.6 - 5.0. The resulting slurry is the precipitated silicon dioxide in the reaction medium.

After a pH below 6.0 has been reached, the slurry is heated for a maturation period at a temperature of 10-30°C above the reaction temperature, and the pH of the reaction mixture is adjusted again as needed. The resulting slurry is then filtered and washed with additional water to remove any by-products such as sodium sulfate that may be contained in the silicon dioxide product. The water content of the obtained wet filter cake is in the range from 60-66% and is a low structure material. The above reaction up to this point is generally the same as described in US patents 3,893,840 and 3,988,162 in the preparation of silicon dioxide prepared from fresh water alkali metal silicate.

In the present method, the material, by filtering and washing the silicon dioxide wet cake, is subjected to a treatment with alkaline earth metal ions to obtain the new abrasive products according to the present invention. According to the present method, the wet washed filter cake is again suspended in its own water or by the addition of additional fresh water at the ambient temperature with stirring. During the stirring, this suspension is then treated with sufficient alkaline earth metal ions, preferably calcium ions, in the form of a salt that is sufficiently soluble to give an amount of alkaline earth metal ions corresponding to 10 to 300 ppm, or 0.001 to 0.03% by weight, calculated on the weight of the dry recoverable silicon dioxide, of alkaline earth metal ions intimately mixed with the silicon dioxide.

The alkaline earth metal ion added at this point is preferably calcium ion because of its ready availability, low cost and ease of incorporation into the silicon dioxide. The calcium ions can be incorporated into the silicon dioxide at this stage in any sufficiently water-soluble form (ie soluble in water in an amount of at least 0.07 g/100 ml of water at 20°C) as in solutions of calcium nitrate, calcium oxide, calcium hydroxide or calcium chloride. Lime or calcium hydroxide is preferred. In addition, solutions of organic salts such as calcium acetate, calcium formate and the like can also be used. The corresponding strontium and magnesium salts of the alkaline earth metal group can also be used. Salts of food quality should be used.

After treatment with the alkali metal ion, the cake suspension is stirred vigorously for 10-20 minutes, preferably 15 minutes, to provide the effective amount of alkaline earth metal for treatment on the surface of the silicon dioxide abrasive. The product formed is then dried. The drying is preferably carried out in a spray dryer at an inlet temperature of 483°C and an outlet temperature of 122°C as known in the art, and then ground to the desired degree of fineness.

The following examples are given to further illustrate the present invention. In the examples, parts are given by weight where otherwise not specifically stated.

Example 1 (comparison example)

In a 30,000 liter stainless steel reactor equipped with a steam jacket, 1,794 liters of sodium silicate solution (3.78% Na2O, 9.53% SiO2) with a specific gravity of 1.121 containing 42 g of Na20 per 1. The reaction medium was heated to 88°C with continuous stirring. At this point, sulfuric acid of 10% concentration (spec

weight 1.066) and sodium silicate solution added simultaneously to the reaction medium at a rate of 151.4 l/min acid and 351 l/min sodium silicate while maintaining the reaction temperature at 88°C - 1°C. These two solutions were added to the reaction medium for a predetermined length of time. The addition of silicate was stopped after 47 minutes, while the addition of acid was continued until the pH of the slurry was between 4.8 and 5.0. The reaction slurry was boiled at 100°C for 20 minutes and its pH was again adjusted to between 4.8 and 5.0. The silicon dioxide slurry formed was filtered and washed to remove most of the reaction by-product (sodium sulfate) and the filter cake was dried, and the dried product was ground to the desired fineness. The dry silicon dioxide was subjected to various physico-chemical tests, the analysis of which is set forth below (see Table I). This example is the preparation of a control product to which no alkaline earth metal was added.

Oak sample 2

To a 30,000 liter stainless steel reactor equipped with a steam jacket was added 1,794 liters of sodium silicate solution (3.78% Na2O, 9.53% SiO2) of specific gravity 1.121 containing 42 g Na2O per 1. The reaction medium was heated to 88 C with continuous stirring. At this point, 10% sulfuric acid (specific gravity 1.066) and sodium silicate solution were added simultaneously to the reaction medium at a rate of 151.4 l/min acid and 351 l/min sodium silicate while the reaction temperature was maintained at 88°C - 1°C . These two solutions were added to the reaction medium for a predetermined length of time. The addition of silicate was stopped after 47 minutes, but the addition of acid was continued until the pH of the solution was between 4.8 and 5.0. The reaction slurry was boiled at 100°C for 20 minutes and its pH was again adjusted to between 4.8 and 5.0. The silicon dioxide slurry formed was filtered and washed to remove most of the reaction byproduct (sodium sulfate).

The washed filter cake was then reslurried without water addition at ambient temperature with stirring. While stirring, the slurry was treated with 102 g of food grade hydrated lime (calcium hydroxide) to provide 25 ppm calcium ion treatment calculated on the total weight of dry, recoverable, solid product in suspension form. After calcium ion treatment, the cake slurry was stirred vigorously for 15 minutes to obtain the effective level of calcium ion treatment on the surface of the silicon dioxide abrasive. The product obtained was then spray-dried at an inlet temperature of 483°C and an outlet temperature of 122°C, ground and measured with respect to abrasive and physical properties in the same way as the abrasive in example 1.

Example 3

The procedure in this example was the same as in example 2 except that the rate of addition of sulfuric acid was 162.7 1 per minute and the calcium addition was 204 9 calcium hydroxide, which gave 50 ppm calcium ion. The product was then examined.

Example 4

This example is the same as example 2 except that the rate of addition of sulfuric acid was 166.5 1 per minute and the calcium addition amounted to 408 g of calcium hydroxide to obtain 100 ppm of calcium ion in the silicon dioxide. The product was then examined.

Example 5

In this example, a silicon dioxide abrasive for dental care products was prepared by first adding 1,420 1 sodium silicate solution (4.09% Na2O, 10.31% SiO2) of specific gravity 1.131 containing 46.3 9 Na2° Pr • 1 ti- 1 the reactor as the react ion medium. The reactor was heated to 91°C with continuous stirring. At this point, 12% sulfuric acid (specific gravity 1.08) and sodium silicate solution were added simultaneously to the reaction medium at a rate of 162.7 l/min acid and 315.7 l/min sodium silicate while the reaction temperature was maintained at 91 - 1°C. The silicate addition was stopped after 47 minutes, but the acid addition was continued until the pH of the slurry was between 4.6 and 4.8. The reaction slurry was boiled at 100°C for 20 minutes and its pH again adjusted between 4.6 and 4.8. The resulting silica slurry was filtered and washed to remove sodium sulfate by-product.

The washed cake was then reslurried without water addition at ambient temperature with stirring. While stirring, the slurry was treated with 510 g of food grade hydrated lime (calcium hydroxide) to provide 125 ppm of calcium ion treatment based on the total weight of the dry recoverable silicon dioxide abrasive present in suspension. After calcium ion treatment, the slurry cake was stirred vigorously for 15 minutes to obtain the effective level of calcium ion treatment on the surface of the silicon dioxide abrasive. The product formed was then spray-dried at an inlet temperature of 483°C and an outlet temperature of 122°C, ground and then examined.

Example 6

This example was the same as Example 5 except that

1,608 L of sodium silicate solution was initially introduced into the reactor as reaction medium and the acid rate was increased to 170.3 l/min, but the silicate rate was maintained at 315.7 l/min.

The washed filter cake was treated with 816 g of calcium hydroxide to obtain 200 ppm of calcium ion treatment on the surface of the silicon dioxide abrasive. The product was then examined.

Example 7

This example was the same as Example 2 except that the calcium ion addition was 2,040 g calcium hydroxide to provide 500 ppm calcium ions. The product was then examined.

After the production of the products in examples 1 to 7, they were examined for physical properties, and the results are shown in table I.

Several representative toothpastes

indicated in the following examples using present field silicon dioxide abrasives.

Example 8

A toothpaste was prepared using the precipitated silicon dioxide abrasive from Example 2 and had the following composition:

The above toothpaste preparation was prepared by mixing the ingredients together in the usual way for toothpaste preparation. Preferably, the water component is introduced first into a suitable container to which is then added with moderate stirring, in order, film-penetrating agents, flavoring agents, humectant and then the remaining ingredients.

A 3:1 by weight slurry of the above freshly prepared preparation with water (3:1 is water to preparation) gives a pH of approx. 7.1.

Such a toothpaste preparation provides beneficial fluoride treatment for dental tissue brushed with it because of the toothpaste's high fluoride compatibility. The toothpaste also provides good cleansing and an RDA of 100. When stored for longer periods at 27°C, such a toothpaste shows minimal loss of soluble fluoride.

Toothpastes that provide substantially similar fluoride treatment benefits, toothpaste-fluoride compatibility, and cleaning ability are obtained when in the preparation in Example 8 the sodium fluoride is replaced with an equivalent amount of stannous fluoride, sodium chlorofluoride, potassium fluoride, potassium stannous fluoride, indium fluoride, zinc fluoride or ammonium fluoride.

Toothpastes that provide substantially similar fluoride treatment benefits and substantially similar cleaning power are obtained when the phosphate salt mixture in the preparation in Example 8 is replaced with an equivalent amount of NaH^PO, , NaH^PO, .-H00, NaH„PO, '2H„ 0, Na„HPO, , 2 q. 2 q. 2 2if2 2 £+ Na2HP0^-2H20, Na2HPO^ • 7H20 , Na3PO^-6H20, Na3P0^-8H20, KH2PO^, K2HPO^, K2HPO^-2H20, K^HPO^-é^O, K3PO^-3H20, K PO^-7H20, K3PO^-9H20, (NH^)H2PO^, (NH^)2HPO^, (NH^)PO^, other mixtures of NaH„P0,-H„0 and Na„HP0,•2H „0 in monosodium to disodium weight ratio 2 q- 2 2 q 2

on from approx. 1:3 to 1:5, mixtures of NaH2P0^-H2O and K2HP0^-2H2O in sodium-to-potassium salt weight ratios of from approx. 1:3 to 1:5, tetrapotassium pyrophosphate, tetrasodium pyrophosphate, disodium pyrophosphate, sodium tripolyphosphate, potassium tripolyphosphate, monopotassium metaphosphate, sodium trimetaphosphate, sodium hexametaphosphate or sodium heptametaphosphate; provided that such preparations give a 3=1 slurry with a pH from 4.0 to 8.0.

Example 9

A toothpaste with a high abrasive content is formulated using the precipitated silicon dioxide abrasive from Example 3 which has the following composition:

Toothpastes that provide substantially similar fluoride treatment benefits, toothpaste/fluoride compatibility, and cleaning effect are obtained when in the preparation in example 9 the field silicon dioxide abrasive component produced as in example 3 is replaced with an equivalent amount of the abrasives produced in examples 2 , 4, 5 and 6.

Toothpastes that provide substantially similar fluoride treatment benefits and substantially similar cleansing effects are obtained when the phosphate salt mixture in the preparation in example 9 is replaced with an equivalent amount of NaH2PO^, NaF^PO^ • H20, NaH2P0^-2H2, Na2HPO^, Na2HPO^ -2H20, Na2HPO^ • 7H?0 , Na^PO^•6H20, Na^PO^-S^O, KH2PO^ , K„HPO, , K0HPO, -2H„0, K„HPO, • 6H O, K „PO, -3H-0, CoP0, -7H_0,

2 4 2 k 2 2 4 2 3 4 2 ' 3 4 2' K3PO^-9H20, (NH^)H2PO^, (NH^)2HPO^, (NH^) PO^, other mixtures of NaH2PO^-H20 and Na2HPO^•2HpO in monosodium to disodium weight ratio of from approx. 1:3 to 1:5, mixtures of NaH„PO, ' WJD oa 2 if 2 K2HP0^-2H20 in sodium-to-potassium salt-weight ratio of from approx. 1:3 to 1:5, tetrapotassium pyrophosphate, tetrasodium pyrophosphate, disodium pyrophosphate, sodium tripolyphosphate, potassium tripolyphosphate, monopotassium metaphosphate, sodium trimetaphosphate, sodium hexametaphosphate or sodium heptametaphosphate, provided such preparations provide a 3:1 slurry with a pH of 4.0 to 8.0.

Example IO

A clear toothpaste is prepared using the precipitated silicon dioxide abrasive from Example 4 which has the following composition:

Example 11

A toothpaste with a low abrasive content is prepared using the precipitated silicon dioxide abrasive from Example 3 which has the following composition:

Toothpastes that give substantially similar fluoride treatment results, toothpaste/fluoride compatibility and cleaning results are obtained when in the preparation in example 10 the field silicon dioxide abrasive component produced as in example 4> is replaced with an equivalent amount of abrasive produced in examples 2, 3 > 5 and 6.

A toothpaste which provides essentially similar fluoride treatment benefits and an improved anti-calculus benefit is obtained when the preparation in example 10 also contains approx. 1.0% by weight disodium ethane-1-hydroxy-1,1-diphosphonate.

Testing and assessment

The aforementioned icium dioxide abrasives according to the invention can be used to produce particularly desirable therapeutic toothpaste preparations containing soluble phosphate membrane film penetrants. Such preparations provide both high abrasive/fluoride compatibility and still have good teeth cleaning effects. The following tests and evaluations serve to show the excellent fluoride compatibility obtained by the field silicon dioxide abrasives according to the invention. It has also been shown above that the abrasives according to the invention provide higher abrasive/fluoride compatibility than similarly produced abrasives which have not been treated so that they contain substantial amounts of alkaline earth material. The excellent cleaning effects of the toothpaste preparations according to the invention are further demonstrated. Finally, it is shown here that the abrasives produced from a sulfate solution acidification process, although they contain an alkaline earth material, do not provide the high fluoride/compatibility values with the "fresh water" field silicon dioxide abrasives according to the invention.

Abrasive/fluoride compatibility

Felt silicon dioxide dental abrasives can be sorted by

its relative compatibility with fluoride materials using a 24 hour abrasive slurry test. Such a test can be used to provide data that can predict the availability of soluble fluoride in certain types of fluoride toothpastes after storage for approx. 4~week period at 27°C.

The 24 hour abrasive slurry test is used to obtain fluoride compatibility values which are defined as the percentage of theoretical maximum available fluoride that is actually measured after 24 hours as soluble fluoride by the following test method.

In this method (Orion Specific Ion Electrode Method), a standard sodium fluoride stock solution containing 1624 ppm fluoride is prepared by dissolving 2.80 g sodium fluoride, 21.5 g NaH2PO^ and 83.4 g Na2HP0^-2H20 in 672.5 g deionized distilled water and stored in a polyethylene bottle. 30 g of this solution is then weighed.

7 g of the silicon dioxide abrasive to be tested is then dispersed in the solution and allowed to remain in it for 24 hours at a temperature of

about. 37.8°C. After 24 hours, the precipitated silicon dioxide abrasive/fluoride solution is centrifuged for 20 minutes at 15,000 r/min or until the supernatant liquid is clear. Then 10 ml of the remaining liquid is pipetted into a plastic bottle. Then, likewise, 10 ml of BOTA/TRAM solution is pipetted into a plastic bottle. (The EDTA/THAM solution is a 0.2 molar in EDTA (a hylenediaminetetraacetic acid disodium salt) and 0.2 molar in THAM (2-amino-2-hydroxymethy1-1,2-propanediol) and adjusted to pH 8.0 with sodium hydroxide). A magnetic stir bar was added and gentle stirring was initiated. The fluoride ion concentration is determined by direct potentiometry at the "Orion" fluoride electrode (model 95-09). Electromotive force is transferred to ppm fluoride in the liquid above by means of a logarithmic equation. The fluoride compatibility value

is then calculated by expressing the measured ppm soluble fluoride as a percentage of the theoretically available soluble fluoride.

Using this method, the relative abrasive/fluoride compatibility values are determined for several abrasives prepared according to examples 1-7. The results of such determinations are given in Table II.

Data in Table II show that the felt silicon dioxide abrasives according to the invention containing special amounts of alkaline earth material provide markedly better abrasive/fluoride compatibility compared to that obtained from an alkaline earth metal-free abrasive material which is otherwise prepared in a similar way. Felt silicon dioxide abrasives prepared as in examples 2-6 should thus be suitable for producing toothpastes containing fluoride and film-penetrating agents that exhibit high abrasive/fluoride compatibility.

Abrasive/fluoride compatibility in toothpastes

Preferred toothpastes according to the invention containing

field silicon dioxide abrasives and membrane cleaning agents were assessed for abrasive/fluoride compatibility. The toothpastes that were prepared for evaluation had the composition of the toothpaste in Example 8 and differed only in the variation of the abrasive content.

To determine the fluoride compatibility value for the tested toothpastes, a soluble fluoride determination method was used, similar to the method described above for determining abrasive/fluoride compatibility values. In this method, the toothpaste preparations are stored for a specific time in a laminate tube. Then place 15.0 g of the preparation in a 100 ml beaker, and then add 45.0 g of distilled water. The mixture is then stirred to form a slurry in which the toothpaste is evenly dispersed. The slurry is then centrifuged for 20 minutes at 15-000 r/min or until the supernatant liquid is clear.

The supernatant is treated as in the abrasive/fluoride compatibility determination method described above. Soluble fluoride concentration is measured in a similar manner, and an abrasive/fluoride compatibility value for each toothpaste is calculated in a similar manner. The toothpaste fluoride compatibility values of the respective toothpastes evaluated are shown in Table III. The assessed abrasives are those which were prepared as described in examples 1-7, and described in table I above.

Data in Table III show that the preferred toothpastes

using the present field silicon dioxide abrasive gives better abrasive/fluoride compatibility values compared to that obtained from a similar toothpaste preparation containing the non-alkaline earth treated field silicon dioxide abrasive prepared by the method of Example 1. Data in Table 1 also show that the soluble fluoride available -ness from the fluorine ion source material is not particularly reduced after

storage when the silicon dioxide abrasives according to the present invention are used in the preferred toothpastes.

Of course, it will be realized that the amount of available soluble fluoride even in the toothpaste preparations

will decrease to some extent as a function of increasing storage time and temperature. Toothpaste/fluoride compatibility values for toothpastes stored for longer periods of time or at more severe temperatures are thus generally lower than those exemplified above.

Additional abrasive/fluoride compatibility data for several toothpastes demonstrating storage for longer periods of time and at higher temperatures is shown in Table IV. Data in Table IV show that the preferred toothpastes according to the invention retain their relatively high fluoride/abrasive compatibility levels even during prolonged storage or under harsh storage conditions.

Properties for cleaning use

The tooth cleaning ability of the silicon dioxide abrasives according to the invention can be assessed by means of "Radioactive Dentin Abrasion" (RDA) testing. The RDA values can be used to judge the relative cleaning performance of different abrasives for any given type of dental abrasive. For felt silicon dioxide abrasives, an RDA value (measured by the method below) of at least 40, preferably between 70 and 120, is thus needed to ensure that the abrasive has sufficient abrasiveness to be an effective dentifrice cleaner. Previously known field silicon dioxide abrasives which do not exhibit high toothpaste/fluoride compatibility are generally poor cleaners for oral care purposes as evidenced by low RDA values. The alkaline earth treated abrasives, however, provide both effective tooth cleaning and high fluoride compatibility.

Several commercial field silica abrasives exhibiting relatively high toothpaste/fluoride compatibility as measured here have been selected for evaluation on RDA values. The test was carried out in a standard toothpaste matrix with the composition of the toothpaste in example 8 which differs only in the variation of the abrasive component.

The procedure used to determine the RDA values for toothpastes listed in Table V is described below. This test method is described more fully in the Journal of Dental Research, July - August 1976, by Hefferren, pages 563-573. The specific steps for determining the RDA values are set out as follows:

A. Selection and preparation of teeth

Healthy single-rooted permanent teeth that are caries-free and viable upon extraction were selected. The teeth are then scraped clean with a scalpel. The crown and root tip of each tooth is removed using a grinding wheel to prepare a dentin sample 14 mm long and at least 2 mm wide at the smallest end. Pieces are cut from the root (dental bone chips) or, alternatively, an additional tooth is also prepared for later use when determining a correction factor for self-absorption of irradiation.

B. Irradiation of dentin

The prepared roots and dentin chips described in step A

was exposed to a neutron current of o 2 x IO <12> neutrons/cm <2> for 3 hours.

C. Installation of roots

After irradiation, the irradiated roots are embedded in a holder

of cold-cured dental methacrylate resin and placed on a cross-brush machine. Toothbrushes used in all experiments are 50-tuft, medium, flat, "Pepsodent" toothbrushes.

D. Preconditioning of the dentin surface

Before the first trial, the freshly mounted, irradiated roots are brushed with a reference slurry (10 g calcium pyrophosphate + 50 ml of a 0.5% CMC-10% glycerol solution) with 6,000 brush strokes.

At the beginning of each subsequent day's trials, the roots are brushed with 1,000 strokes.

E. Sample

After preconditioning, the dentin samples are then conditioned with the reference slurry (same slurry as in step D) with 1,500 brush strokes at the beginning, during and at the end of each trial run. The trial consists of brushing dentin samples with 1,500 brush strokes with a slurry of test product (25 g tooth care agent + 40 ml deionized distilled water).

F. Preparation of correction factors

The correction factors are prepared by dissolving the tooth chips, or alternatively a further tooth, from step B in 5 ml of concentrated hydrochloric acid brought to a volume of 250 ml with distilled water. 1 ml of this solution is added to test pastes and reference slurries prepared similarly to those in step E, and then neutralized with 0.1 N sodium hydroxide.

Radioactive tracer count

The radioactivity of the slurry samples (1.0 ml) is determined by an "Intertechnique SL-30 liquid seintillation counter". Alternative counting method: 3 ml samples of each slurry over

transferred to flat-bottomed 25 mm x 7.9 mm stainless steel disks and counted using the "Nuclear Chicago Geiger Counting System".

Calculations

The radioactive dentin abrasive value (RDA) for a particular paste will be the ratio of the mean of the corrected counts for that paste to the mean value of the reference multiplied by 100. The reference abrasive is given an arbitrary dentin abrasion value of 100 units.

The result of such RDA value determinations is given in Table V.

Data in Table V show that the commercial field silicon dioxide abrasives may well exhibit high abrasive/fluoride compatibility, but are not sufficiently abrasive so that they can be useful as dentifrice abrasives. Surprisingly, the present new field silicon dioxide abrasives provide excellent abrasive/fluoride compatibility and yet at the same time provide excellent RDA abrasive values, which values can be used as an indicator of relative teeth cleaning performance.

"Freshwater"- compared to "sulphate liquid"- abrasives

As indicated above, the abrasives according to the present invention are related to, but clearly different from, the calcium-treated silicon dioxides according to Norwegian patent application 773160. In order to show such a difference, the following evaluation was carried out for

to compare the fluoride compatibility of the products according to

Norwegian patent application 773160 with that for the abrasive products according to the invention. The "sulfate liquid" silicon dioxide materials that were tested were prepared according to the method set forth in Norwegian patent application 773160 and US patent 3,960,586 by the following method: Dry sodium sulfate was added to 37.85 1 of water in a 757 1 reactor so that the sodium sulfate concentration in the reaction medium was 10%. The pH of the reaction medium was then adjusted to 9.0 by adding sodium silicate. The reaction temperature was 65°C. The sodium silicate solution had a SiO 2 /Na 2 O molar ratio of 2.5 and a concentration of 24-0 g/l. Sodium silicate was added to the reaction medium for 4 minutes. At this point the sodium silicate addition was stopped and 11.4% sulfuric acid was added to the reaction medium until a pH of 9.0 was reached. At this point, the sodium silicate solution and the sulfuric acid solution were added simultaneously for 35 minutes. At the end of the 35 minute addition of silicate, the silicate addition was stopped, and the acid oxygen addition was continued until a slurry of pH 5.5 was obtained. The batch was matured at 77°C for 20 minutes, and the resulting wet cake was recovered and washed.

The wet cake was then treated as described in example 2

of the present description, divided into 6 separate portions and treated with 50, 100, 200, 400 and 800 ppm calcium from aqueous solutions of calcium hydroxide. Each wet cake was then dried and

treated as described in example 2 and characterized in the following table VI where the first abrasive is a control in which no calcium was added. Table VI indicates the results of such an assessment.

As will be seen from the data in Table VI, the calcium-treated "sulphate liquid" abrasives according to Norwegian patent application 773160 give abrasive/fluoride compatibility values which are generally lower than those obtained from the "freshwater" silicon dioxide abrasives according to the present invention (see table In f).Furthermore, the addition of an alkaline earth metal to the abrasives prepared by the "sulphate liquid" method does not lead to a dramatic improvement in abrasive/fluoride compatibility. On the contrary, as will be seen by comparison with Table II, the addition of equivalent amounts of alkaline earth metal to the silicon dioxide abrasives of the invention prepared by the "fresh water" method to dramatic improvements in abrasive/fluoride compatibility.

Claims (11)

1. Abrasive preparation for dentifrices, in particular for toothpastes, comprising a field, amorphous silicon dioxide prepared by acidifying a fresh water alkali metal silicate solution and containing alkaline earth metal ions, characterized in that the silicon dioxide has been intimately reacted with a compound of an alkaline earth metal so that there are 10-300 ppm alkaline earth metal ions in it and intimately associated with it, the amorphous silicon dioxide having an RDA value ("Radioactive Dentin Abrasion" value) of at least 40, a bulk density of 0.24-0.55 g/ml, an oil absorption of 70-95 cm<3>/100 g, a BET surface area of 100-250 m<2>/g, a loss on ignition of 4- 6% and an average particle size of 5-15 µm, and in that the abrasive preparation, when used in toothpastes containing a therapeutic fluoride agent, provides a paste that exhibits minimal loss of soluble fluoride when stored at normal temperatures, and a fluoride compatibility for the toothpaste of at least 90%. 2. Abrasive preparation according to claim 1, characterized in that the alkaline earth metal ions are from the group calcium, strontium and magnesium. 3. Abrasive preparation according to claim 1 or 2, characterized in that the amount of alkaline earth metal ions present is 10-100 ppm. 4. Abrasive preparation according to claims 1-3, characterized in that the alkaline earth metal ions are calcium ions. 5. Method for producing an abrasive preparation according to claim 1, where a) an aqueous solution of an alkali metal silicate with a molar ratio SiO2:X20 of 2.0-2.7, in which X denotes an alkali metal, is prepared at a reaction temperature of 77-91 C, b) the alkali metal silicate solution is acidified with a mineral acid until the precipitation of silicon dioxide is essentially complete, after which the mineral acid addition continues until the pH is 6.0 or below, c) digestion is carried out by heating at a temperature of 10- 30°C higher than the reaction temperature, for 10-30 minutes, and d) the resulting slurry is filtered, and the solid product washed with fresh water, characterized in that e) the obtained wet cake is again reslurried in water and under stirring conditions, f) a sufficient amount of alkaline earth metal ions is added in the form of a sufficiently soluble alkaline earth metal compound in a sufficient amount so that the wet cake . alkaline earth metal ions are added in an amount of 10-300 ppm, based on the dry extractable product in the slurry, g) the resulting mixture is stirred so that the effective amount of the alkaline earth metal adheres to the surface of the silicon dioxide, and h) the solid abrasive preparation is dried and extracted. 6. Method according to claim 5, characterized in that sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid or carbonic acid is used as mineral acid. 7. Method according to claim 5 or 6, characterized in that only part of the alkali metal silicate is used as a receiving solution for the mineral acid, and that the rest is added to the alkali metal silicate solution at the same time as the mineral acid. 8. Method according to claims 5-7, characterized in that calcium, strontium or magnesium ions are used as alkaline earth metal ions. 9. Method according to claims 5-8, characterized in that calcium, which is added as calcium hydroxide, calcium oxide,. calcium nitrate or calcium fluoride are used as alkaline earth metal ions. 10. Method according to claims 5-9, characterized in that the alkaline earth metal salt reacts with the wet cake slurry at ambient temperature. 11. Method according to claims 5-10, characterized in that sodium silicate is used as an alkali metal silicate, that the acidification is carried out with sulfuric acid, and that the alkaline earth metal ion is added in the form of calcium hydroxide to give 10-100 ppm calcium ions intimately reacted with the silicon dioxide product.